The present invention relates to a radiation-sensitive recording material, in particular for producing planographic printing plates, composed of a layer support and a positive-working, radiation-sensitive layer having a rough surface and containing at least one 1,2-quinonediazide as the radiation-sensitive compound and a polycondensate or polymer as a binder insoluble in water and soluble or swellable in aqueous-alkaline solutions and a filler.
Recording materials of this type are known. For planographic printing applications, the layer weight of the radiation-sensitive layer of these materials is generally below about 3 g/m.sup.2, and the processing comprises process steps of bringing the film original and the recording material into contact by evacuation, exposing by means of UV light, developing with an alkaline developer, gumming the planographic printing plate produced and, if appropriate, baking the plate.
In order to ensure, on the one hand, rapid contacting of the film original and planographic printing plate and, on the other hand, to minimize air occlusions during the evacuation and/or adequately to ensure removal of the nitrogen during the diazo photolysis, i.e., to induce the uniform contacting that is required for an exact transfer of screen dots, it has proved to be advantageous to use materials having a rough surface.
A rough surface can be produced by the user immediately before the processing of the recording material, for example, by dusting with a powder. This procedure has, however, not gained acceptance for a variety of reasons, such as uneven copying results.
Attempts have therefore been made by the manufacturers of pre-sensitized planographic printing plates to provide their products during the manufacturing process with a defined rough surface. Thus, the embossing of the layer surface or the washing-out of water-soluble particles from the light-sensitive layer has already been disclosed (U.S. Pat. No. DE 1,813,445, corresponding to GB 1,293,161). It is also known to provide the layer with an added blowing agent that is activated during the drying process (EP 0,011,648, corresponding to U.S. Pat. No. 4,371,602). It is also known to add resins that agglomerate during the drying process to the light-sensitive layer (U.S. Pat. No. DE 2,948,737, corresponding to GB 2,043,281). None of these processes has, however, gained acceptance in the production of planographic printing plates.
On the other hand, the application of a dulling layer to the radiation-sensitive layer has proved to be a feasible approach such as, for example, the application of filled, developer-soluble dulling layers (U.S. Pat. No. DE 3,009,928, corresponding to GB 2,046,461). The application of unfilled, discontinuous dulling layers, applied by means of rollers having a rough surface, is also known (U.S. Pat. No. DE 2,606,793, corresponding to U.S. Pat. No. 4,216,289). Finally, developer-soluble dulling powders can also be dusted on and fixed (U.S. Pat. No. DE 3,003,131, corresponding to U.S. Pat. No. 4,288,521). It is also known to spray on aqueous solutions or dispersions of developer-soluble resins (U.S. Pat. No. DE 3,131,570, corresponding to GB 2,081,919) and to dry them. Dulling layers can also be sprayed on by an electrostatic method (EP 0,344,985). It is also known to spray on dulling layers that have essentially the same composition as the radiation-sensitive layer (U.S. Pat. No. DE 3,433,247, corresponding to U.S. Pat. No. 4,842,982).
By means of these techniques, it is possible to produce planographic printing plates that prove to the outstanding for processing in contact-printing. This is however, contrasted by the disadvantage that, even if developer-soluble dulling layers are used, a lower developing speed and an increased developer consumption are found, and considerable additional production costs arise due to the additional layer.
These points were the incentive for a search for possible ways of providing the radiation-sensitive, positive resist layer with a rough surface directly during the manufacturing process.
In U.S. Pat. No. DE 2,926,236 (corresponding to CA 1,148,014), the addition of inorganic or organic fillers having a mean particle diameter of 1 to 20 .mu.m is described for this purpose.
It is also known that the advantage of easy dispersibility of the fillers insoluble in the coating solvents is obtained either if thermally cured phenol/formaldehyde resin is used as filler (U.S. Pat. No. DE 3,117,702, corresponding to GB 2,075,702) or if silica particles having a hydrophobic surface and a particle diameter of less than or equal to 0.5 .mu.m are added to the above filler (JP 75 115,548).
None of these measures, however, has provided optimum results, since these materials are unable to meet the following requirements simultaneously:
(a) an evacuation time that is comparable to that obtained when a dulling layer is used, PA1 (b) a susceptibility to air occlusions that is low and a uniform screen transfer (screen evenness) as in the materials with dulling layers, PA1 (c) a resolving power and associated possibility of light correction, i.e., for film edge elimination by means of high exposure, without losses in fine-line parts or highlight parts, that is unaffected as much as possible, and PA1 (d) absence of halo formation around the filler particles or other cosmetic defects which adversely affect the functional behavior.